1. Field of the Invention
The present invention relates to a battery-driven hydraulic excavator for performing various operations by electric power from a mounted battery.
2. Description of the Related Art
Japanese Utility Model Application Laid-Open No. Hei 4(1992)-53846 discloses a battery-driven type working machine for performing public works or the like by electric power from the battery. In this working machine, an electric motor is driven by electric power from the battery. A hydraulic pump is driven when the motor is driven. A hydraulic motor is driven by operating oil discharged from the hydraulic pump. The excavator is operated when the hydraulic motor is driven.
As compared with the working machine of an internal combustion engine type using an internal combustion engine such as a gasoline engine, a Diesel engine or the like as a driving source, the aforementioned battery-driven type working machine produces less noises and does not discharge exhaust gas. Therefore, such a working machine is suitable for operation in city areas where buildings are thickly settled.
Incidentally, in the battery-driven type working machine, since the storing ability of battery as an electric power source of an electric motor is not higher in energy conversion than the fuel storing ability of the internal combustion engine type working machine, the battery-driven type working machine cannot withstand the use for a long period of time, compared with the internal combustion engine type working machine. In the working machine disclosed in Japanese Utility Model Application Laid-Open No. Hei 4(1992)-53846 for solving the problem as noted above, switching between a battery power source and a commercial power source can be made. In this working machine, when the commercial power source is present in the operation spot, the commercial power source is used, and only when the commercial power source is not present, the battery power source is used.
However, for such a working machine, a very long lead wire is necessary to supply electric power from the commercial power source. Further, it is necessary that a device for winding the lead wire is mounted on the working machine so as not to get in the way of operation so that the lead wire may appear as the working machine moves. This increases the cost for the working machine. Further, when the machine is rotated, the lead wire gets entangles with an upper rotating body to impede workability.
Further, in the working machine disclosed in Japanese Utility Model Application Laid-Open No. Hei 4(1992)-53846, since the electric energy supplied from the battery to the electric motor cannot be adjusted, a fixed electric power is always supplied to the electric motor. Thereby, the operational speed of an operating member is constant under the same load. Accordingly, the operation according to the situation cannot be accomplished.